Plastische Querschnittstragfähigkeit von quadratischen und rechteckigen Hohlprofilen

Plastic resistance of square and rectangular hollow sections. The plastic resistance of rectangular hollow sections is usually determined by using approximation formulae or simplified models. These approximations lead to a accuracy, which depends on the dimensions h, b, t and the size of the rounded corners. Applying these approximations the plastic resistance is sometimes significantly under‐ or overestimated. The present paper deals with the development of verifications and simplified approximations of high accuracy for the plastic resistance. The new procedures are qualified for the analysis of any combination of the internal forces and moments N, V_y, V_z, M_x, M_y and M_z. In addition the verifications according to DIN EN 1993‐1‐1 are modified concerning the accuracy and the expansion of the application area.     

Querkrafttragfähigkeit von Fahrbahnplatten ohne Querkraftbewehrung

Es wird über Versuche zur Querkrafttragfähigkeit von Brückenfahrbahnplatten aus Stahlbeton berichtet. Diese zeigen, dass die bekannten Rechenansätze für Bauteile ohne Querkraftbewehrung nach DIN 1045‐1 bzw. DIN‐FB 102 für Fahrbahnplatten auf der sicheren Seite liegen, die tatsächliche Tragfähigkeit aber weit unterschätzt wird. Weitere Ansätze zur Berechnung der Querkrafttragfähigkeit von Stahlbetonbauteilen ohne Querkraftbewehrung werden erörtert. Während die Modelle bei der Auswertung einer Datenbank von Balkenversuchen eine gute Übereinstimmung aufweisen, zeigt der Vergleich mit den Modellversuchen, dass die meisten Rechenverfahren die Tragfähigkeit der Platten unterschätzen. Zur Berechnung der Querkrafttragfähigkeit von Platten ohne Querkraftbewehrung unter Punktlasten wird ein Modell vorgeschlagen, welches die Querkrafttragfähigkeit mit der Zugbeanspruchung der Biegezugzone im kritischen Bereich verknüpft. Shear Resistance of Bridge Decks without Transverse Reinforcement The design of concrete bridge deck slabs is of major concern since the introduction of the Eurocodes as the calculated shear capacity of slabs without stirrups and staggered reinforcement according to the new design standards is often considerably smaller compared to the former regulations i.e. DIN 1045:88. This raises the question whether the existing structures are still save. A series of 12 tests on 4 different specimens representing a bridge deck was performed to examine the real load bearing behaviour of a slab with and without shear reinforcement under a wheel (point) load. The evaluation of the test results revealed, that the current design formula with an assumed elastic shear force distribution leads to rather conservative values of shear capacity for bridge deck slabs. Various approaches for shear design are discussed and the accuracy is checked by means of a shear database and the test results. A new model to calculate the shear capacity is proposed which shows a better agreement with test data than the known approaches.     

Ein “Overall‐Konzept” für die Querschnittstragfähigkeit im elasto‐plastischen Bereich

Es wird die bereits für andere Tragfähigkeitsprobleme von Bauteilen (Knicken, Beulen) entwickelte “Overall‐Methode” auf die Berechnung der Querschnittstragfähigkeit von Stahlprofilen angewendet. Dies führt zu einer neuen Berechnungsmethode, die den gesamten elasto‐plastischen Bereich ohne die Notwendigkeit einer Klasseneinteilung umfasst. Basierend auf zahlreichen Versuchen und Querschnittsberechnungen mittels geometrisch, materiell nichtlinearer Analysen mit Imperfektionen werden (analog den Knicklinien) Bemessungskurven für die Abminderungsfaktoren vorgeschlagen, die für bestimmte Querschnittstypen wie I‐beziehungsweise H‐Profile oder Rechteck‐Hohlprofile, einen einheitlichen Verlauf im elasto‐plastischen Bereich aufweisen. An overall concept for the cross‐section resistance in the elasto‐plastic range. The “overall method” which has been developed for other load carrying problems of steel members (e.g. lateral member buckling or buckling of shells) is applied to the calculation of the cross‐section resistance of steel members. This leads to a new procedure that covers the whole elasto‐plastic range without the need of cross‐section classification. Based on numerous experimental tests and numerical calculations (GMNIA) design curves for the reduction factors of I‐ and H‐shaped sections and RHS‐sections are proposed that show a consistent transition in the elasto‐plastic range.     

Zum Ermüdungsverhalten von X‐Knoten aus quadratischen Hohlprofilen

Fatigue behaviour of X‐joints made of rectangular hollow sections. In 1984 Mang and Bucak ([8], [9]) presented their first detailed proposal for FAT‐classes for welded X‐sections made of rectangular hollow sections (RHS) to the committee of regulations for the DIN EN 1993‐1‐9 [1]. The proposal was based on experimental investigations of welded X‐joints of RHS with different width (b/b_o) and thickness (t_o/t) ratios, but were not accepted because the scope of the Eurocode 3 regulation should not be enlarged at that time. There are no FAT‐classes for welded X‐sections made of RHS in the current version of DIN EN 1993‐1‐9 [1], the IIW document [2] and the FKM guideline [4] for a nominal stress approach. There are specifications in the crane construction code DIN EN 13001‐3‐1 [3] but they are very conservative. CIDECT Design Guide No. 8 [12] also does not contain information referring this issue based on the nominal stress concept, but it gives detailed specifications like assessment formulas and graphs for the determination of the stresses (SCF) and strains (SCNF) for welded rectangular and hollow sections on the base of the structural stress concept. At the university of applied sciences Munich and the Labor für Stahl und Leichtmetallbau GmbH, Kissing, further investigations in the research project [13] were executed upon request of several industrial partners with focus on the fatigue behaviour of welded X‐sections made of RHS. Based on the results, a verification and extension of the code proposal of Mang and Bucak ([8], [9]) has been prepared. The main focus of this new investigation was the fatigue behaviour of bigger thickness ratios (t_o/t ≥ 2,0) as well as actual tube grades and welding procedures with high process reliability. This article summarizes the results and the #new code proposal.